This invention relates to a filtering device and, more particularly, to a filtering device suitable for precision filtering in a state submerged in liquid to be treated. Liquid to be treated includes water for general uses, drinking water, river water and pool water.
Known in the art of filtering devices is one which employs a plurality of filter tubes. In this filtering device, a plurality of filter tubes are provided in parallel in a container. Liquid to be treated is introduced from an inlet provided in one end portion of the container via a pump and filtered through these filter tubes and treated liquid is delivered out of a treated liquid outlet provided in the other end of the container.
For the filter tubes used in the prior art filtering device, filter elements for precision filtering which consist of a porous material or a filter cloth having densely formed pores are used. In these filter elements, however, pores of these filter elements are blocked by fine powdery solid particles suspending the liquid to be treated in a relatively short period of time after starting of operation of the filtering device with the result that filtering efficiency is rapidly dropped. For this reason, the filtering operation of the filtering device has to be stopped for performing reverse washing of the surface of the filter elements and resumed after removing the materials which have blocked the pores of the filter elements. Such stopping of the filtering operation and performing of reverse washing need to be repeated frequently during the filtering operation with resulting decrease in the working efficiency. Besides, the blocking of the inside of pores of the filter elements advances notwithstanding the repetition of reverse washing until at last it becomes necessary to take out all of the filter elements from the filter tubes and replace them by new filter elements.
It is, therefore, an object of the present invention to provide a novel high precision filtering device having a high filtering efficiency which is capable of preventing blocking of filter elements while continuing the filtering operation without stopping the filtering operation for performing reverse washing.